The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine constructed for sucking evaporated fuel generated in a fuel tank into an intake side of the internal combustion engine so as to burn the evaporated fuel.
There has been an apparatus in which evaporated fuel generated in a fuel tank is stored in a canister, and the evaporated fuel stored in the canister is discharged together with air to an intake side of an internal combustion engine so as to be burnt, in which the quantity of discharged fuel, i.e., canister purge quantity is varied by a fixed value and concentration of the evaporated fuel sucked into the intake side of the internal combustion engine from the canister is detected by the variation of an air-fuel ratio at that time, thereby to correct an air-fuel ratio learning value in accordance with this concentration (e.g., JP-A-2-130240).
In a conventional apparatus described above, however, there is a problem that correct air-fuel ratio learning in a plurality of learning areas (both in idling and non-idling in particular) cannot be sufficiently be done since the concentration of the evaporated fuel is high at the initial stage of purging, and the variation of an air-fuel ratio feedback value due to the influence by the evaporated fuel becomes larger than the variation of the air-fuel ratio feedback value to be learnt, and the concentration of the evaporated fuel has not yet been detected correctly at the initial stage of the start of purging.
A U.S. patent application Ser. No. 52926 entitled "Air-Fuel Ratio Control Apparatus of Internal Combustion Engine" was filed on Apr. 27, 1993 on the basis of Japanese patent application No. 4-109592 and assigned to the present assignee.